Method of heat-treating electroplated material



Patented Mar. 25, 1947 METHOD OF HEAT-TREATING ELECTROPLATED MATERIAL John S. Naohtman, Youngstown, Ohio Application March 30, 1942, Serial No. 436,782

8 Claims.

The invention relates generally to the heat treatment of material electroplated with metals or alloys having low melting points, and more particularly to a method of heat treating strip steel electroplated with tin or tin alloys in order to brighten and improve the coating.

Prior practice includes heat treating metal in a non-oxidizing or reducing atmosphere such as hydrogen or carbon monoxide, but where strip metal is heat treated continuously, the use of such atmospheres is very expensive and requires excessively long periods or long heat treating chambers or both. Moreover, such atmospheres are not well adapted for heat treating electroplated coatings such as tin and tin alloys, because of the rapid temperature changes required to be made in the coated strip.

In order to brighten and improve the quality of the matte-like surface which is characteristic of electroplated tin coatings, in a minimum amount of space, I have determined that it is desirable first to heat the coated strip rapidly and uniformly in a non-oxidizing hydrocarbon medium to a temperature just below the melting point of the tin coating, and then quickly to raise the temperature of the coating while in said medium to slightly above the melting point of tin for a short time to melt the coating. While still in the non-oxidizing medium and without contacting anything else, the coated strip is then rapidly cooled to a temperature below the temperature at which the tin coating will oxidize, before being exposed to the atmosphere.

A method of brightening a tin or tin alloy coating, by heat treating the coating with a hydrocarbon medium which boils below the melting point of tin and preferably between 300 F. and 440 F., including passing the coated material through the hydrocarbon medium maintained in a liquid state and then through the vapor of said medium, is the subject of a separate application filed by me on March 20, 1942, Serial No. 436,783, and entitled Heat treatment of electroplated strip metal.

The subject of this application is a novel method of heat treating an electroplated tin of tin alloy coating, by using a hydrocarbon medium which boils below the melting point of tin but preferably below 300 F., and passing the coated material directly through the heated vapor of said medium for melting the coating, without first passing it through the medium in, a, liquid state.

It is a general object of the present invention to provide a novel method for brightening elec troplated tin or tin alloy coatings. I

for rapidly heating and cooling electroplated strip continuously to brighten the coating.

A still further object is to provide a novel atmosphere for heat treating electroplated material.

These and other objects are accomplished by heating the vapor of a non-oxidizing medium consisting of one or more hydrocarbons and boil ing below the melting point of tin and preferably below 300 F., passing a strip electroplated with tin through said heated vapor to rapidly and um formly preheat the strip and then momentarilyto melt the coating, and then immediately cooling the strip to below the temperature at which the coating will oxidize before exposing it to the atmosphere.

Referring to the'drawing forming part hereof, the figure is a more or less diagrammatic cross sectional view of a preferred embodiment of apparatus for carrying out the invention.

In the drawing, the strip S, which has been previously electroplated with tin,rinsed and dried, is shown passing over the roll l0 and entering the heat treating apparatus. The strip S may be preheated by the drier to say 200 F. to 225 F. as it reaches roll it. Suitable means (not shown) are provided for propelling the strip through the heat treating apparatus.

From roll II] the strip S passes downwardly through a seal I I, which may be of soft material such as synthetic rubber or asbestos, and then into a bottom roll chamber l2 where it passes around a roll l3 and then upwardly through a slot I4 in partition wall I5 into an elongated preferably vertical preheating chamber It. The strip passes upwardly from preheating chamber [6 through a slot I! in a partition wall l8 and into a top roll chamber l9.

In chamber 19 the strip passes over a top roll 20 and then downwardly through slot 2| in wall l8 into a preferably vertical fusing chamber 22, from which it passes downwardly through a slot in partition wall 23, and then downwardly through a cooling chamber 24.

The chambers I2, [6, I9, 22 and 24 are all filled with the vapor of a hydrocarbon medium which boils below the melting point of tin, and preferably below 300 F. The hydrocarbon medium is preferably a saturated or unsaturated aliphatic hydrocarbon or an aromatic hydrocarbon or a with molten tin.

the present invention may for example be a pemixture of two or more of said hydrocarbons, which boils below 300 F., and which does not deposit carbon film or smudge when in contact with molten tin. Saturated and unsaturated hydrocarbons and mixtures thereof include alkanes having a carbon chain of three or more atoms, olefins, and petroleum solvents. Aromatic hydrocarbons include coal tar fractions or solvents.

Petroleum and coal tar fractions in this boiling range'are light hydrocarbons as distinguished from heavy oils, and have high rates of thermoconductivity as compared with heavy oils, but do They have high thermostabilit'y' 4 formly raise and lower the temperature of the strip as required.

As the strip passes through the cooled liquid bath in quenching tank 21, it is cooled below the solidification temperature of the coating or below about 435 F. before contacting roll 32 submerged in the bath, so that the roll 32 does not mar the coating surface. As the strip passes around roll 32 and leaves the liquid pentane,. it is cooled below the oxidation temperatureof the tin coating before passing out of the hood 33 into the atmosphere and'over exit roll 34.

the soldering temperature of tin, so that no r 1 smudge is left when said fractions arein contact The hydrocarbon medium of troleum fraction comprising pentane, which boils at about 97 F. and has high thermoconductivity and high thermostability. Pentane'will not decompose or crack when heated to the soldering temperature of tin and will not leave a carbon smudge when evaporated from the tinned surface. Preferably liquid pentane is taken from a storage tank, at a convenient location remote from the heat treating apparatus and piped to a suitable vaporizer from which pentane vapor at a tem perature of about 100 F. to 125 F. is piped to inlet 2 5where it is introduced into the cooling chamber 24. Liquid pentane is also taken from the storage tank and cooled to below 97 or preferably about '75? F., and then pumped to inlet 26 where it is introduced into-a quenching tank 21 communicating with the bottom end of cooling chamber 24, and the cooled liquid pentane provides a bath having a liquid level L, into which the strip S- passes on leaving cooling compartment 24.

If desired, the pentane vapor may be introduced at suitable temperatures into any of the preheating, fusing and cooling chambers by means of sprays or jets directed against the strip.

Th pentane vapor entering at inlet 25 fills cooling chamber 24, fusing chamber 22, top roll chamber l9, preheating chamber I6 and bottom roll chamber l2. Any of the vapor condensed in cooling chamber 24 will drain into quenching tank'21. In the preheating chamber heating elements 28 are mounted on the walls on opposite sides of the strip, and the amount of heat supplied by heating elements '28 is controlled to raise the temperature of the strip S to just belowthe melting point of tin, or to about 440 F., by the time it passes over top roll 20 in chamber l9.

Heating elements 29 are mounted on the walls of the fusing chamber 22 on opposite sides of the strip, and the amount of heat supplied by heating elements 29 is controlled to raise the temperature of the strip S to slightly above the melting point of tin, or to about 450 to 470 F., in order to melt and flow the coating to brighten the same. Accordingly, the hydrocarbon medium used must be one which will not leave a smudge or deposit on the strip.

In the cooling compartment 24, cooling coils 30 are mounted on opposite sides of the strip for immediately cooling the coating to below its solidification temperature, before the strip contacts anything. Preferably, circulation fans 3! are mounted in the preheating, fusing and cooling chambers I6, 22 and 24 respectively, to keep the,

pentane vapor constantly circulating and uni;-

Preferably a small amount (say one-half per cent by weight) of palm oil or other vegetable oil is added to the liquid pentane in tank 21, and the strip passes through squeegee rolls 5-35 in the hood 33 to remove excess film and spread the remaining film uniformly over the surface of the coating; As the strip emerges from hood 33 into the atmospher the pentane in the film will evaporate, leaving an imperceptible oil filmon the coating. which is desirable for future operations on the strip.

A drain pipe 36 is provided at the bottom of tank 21 so that the liquid pentane may be drawn,

off, cooled, and returned through inlet 26 to maintain the temperature of the quenching bath within a desired range.

The strip carrying rolls l0, i3, 20, 32 and 34 l are made of suitable material such as polished steel or polished chrome, plated steel, which will by way of example, and the invention defined in the claims may be carried out in modified forms of apparatus wherein the strip passes through preheating,- fusing and cooling chambers disposed substantially horizontal or at slight angles to the horizontal, instead of vertical as shown herein.

The term hydrocarbon medium as'used herein is not limited to pentane, but includes saturated and unsaturated aliphatic hydrocarbons and aromatic hydrocarbons, or a mixture of two or more of said hydrocarbons, which boils below the melting point of tin and preferably below 300 F., and which will not deposit carbon film or smudge when in contact with molten tin.

While I have described the heat treatment of electroplated strip metal, the invention may be applied to other coated products such as strip sheets, sheets, wire and the like, without departing from the scope of the invention as defined in the appended claims.

I claim: v

1. The method of heat treating material electroplated withv a coating of tin for brightening the tin surface, which includes vaporizing a by drocarbon medium selected from the group of-petroleum and coal tar fractions which boil between about 97 F. and 300 F., passing the material continuously through successive portionsof said vaporized hydrocarbon medium, heating a firstsaid portion of said medium to preheat the mate-- rial to a temperatureiust below the melting point of tin, heating a second said portion of said medium to raise the temperature of th material slightly above the melting point of tin to melt the tin coating, and cooling a third said portion of said medium to a point above the vaporizing temperature of the medium but below the melting point of tin to solidify the tin coating.

2. The method of heat treating material electro-plated with a coating of tin for brightening the tin surface, which includes vaporizing a hydrocarbon medium of high thermoconductivity and high thermostability which boils between about 97 F. and 300 F., passing the material continuously through successive portions of said vaporized hydrocarbon medium, heating a first said portion of said medium to preheat the material passing therethrough to a temperature just below th melting point of tin, heating a second said portion of said medium to raise the temperature of the material passing therethrough slightly above the melting point of tin to melt the tin coating, cooling a third said portion of said medium to a point above the vaporizing temperature of the medium but below the melting point of tin to solidify the coating on the material passing therethrough, and then passing the material through a bath of said medium contacting with said third medium portion and cooled to a liquid state to cool the tin coating below its oxidizing temperature.

3. The method of heat treating material electro-plated with a coating of tin for brightening the tin surface, which includes vaporizing a hydrocarbon medium of high thermoconductivity and high thermostability which boils between about 97 F. and 300 F., passing the material continuously through successive portions of said vaporized hydrocarbon medium, heating one said portion of the medium to raise the temperature of the material slightly above the melting point of tin to melt the coating, and cooling a successive said portion of said medium to a point above the vaporizing temperature of the medium but below the melting point of tin to solidify the tin coating.

4. The method of heat'treating material electroplated with a coating of tin for brightening the tin surface,which includes vaporizing a hydrocarbon medium of high thermoconductivity and high thermostability, which boils between about 97 F. and 300 F., passing the material continuously through successive portions of said vaporized hydrocarbon medium, heating one said portion of said medium to raise the temperature of the material slightly above the melting point of tin to melt the coating, cooling a successive said portion of the medium to a point above the vaporizing temperature of the medium but below the melting point of tin to solidify the tin coating, and then passing the material through a bath of said medium communicating with said vaporized portions, said bath being cooled to a liquid state to cool the tin coating below its oxidizing temperature.

5. The method of heat treating material electroplated with a coating of tin for brightening the tin surface, which includes the steps of passing the material in a first closed space through the vapor of a hydrocarbon medium of high thermoconductivity and high thermostability which boils between 97 F. and 300 F. and maintained at a temperature just below th melting point of tin to preheat the coating, then passing the material in a closed space through said hydrocarbon vapor maintained at a temperature above the melting point of tin to melt the coating, and then passing the material in a closed space through a bath of said hydrocarbon medium cooled to a liquid state to solidify the coating, all without exposing the material to the atmosphere.

6. The method of heat treating material electroplated with a coating of tin for brightening the tin surface, which includes the steps of passing the material in a first closed space through the vapor of a hydrocarbon medium selected from the group of petroleum and coal tar fractions which boil between about 97 F. and 300 F. and maintained at a temperature above the melting point of tin to melt the coating, and then in a second closed space communicating with said first closed space passing the material through a bath of said hydrocarbon medium cooled to a liquid state to solidify the coating, all without exposing the material to the atmosphere.

7. The method of heat treating material electroplated with a coating of tin for brightening the tin surface, which includes the steps of passing the material in a first closed space through the vapor of a hydrocarbon medium comprising a petroleum fraction which boils between about 97 F. and 300 F. and maintained at a temperature above the melting point of tin to melt the coating, and then in a second closed space communicatingwith said first closed space passing the material through a bath of said hydrocarbon medium cooled to a liquid state to solidify the coating, all without exposing the material to the atmosphere.

8. The method of heat treating material electroplated with a coating of tin for brightening the tin surface, which includes the steps of passing the material in a first closed space through the vapor of a hydrocarbon medium comprising a coal tar fraction which boils between about 97 F. and 300 F. and maintained at a temperature above the melting point of tin to melt the coating, and then in a second closed space communicating with said first closed space passing the material through a bath of said hydrocarbon medium cooled to a liquid state to solidify the coating, all without exposing the material to the atmosphere.

JOHN S. NACH'IMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,240,265 Nachtman Apr. 29, 1941 1,517,910 Kirschner Dec. 2, 1924 2,357,126 Nachtman Aug. 29, 1944 FOREIGN PATENTS Number Country Date 448,288 British Feb. 26, 1935 457,780 British Dec. 4, 1936 

